Simplify .NET multi-platform Dockerfile (dockersamples#301)

* Improve dotnet multiplatform dockerfile

* Use implicit TARGETPLATFORM

Author: lbussell

worker/Dockerfile

@@ -8,27 +8,16 @@
 # docker buildx build --platform "linux/arm64/v8" .
 FROM --platform=${BUILDPLATFORM} mcr.microsoft.com/dotnet/sdk:7.0 as build
 ARG TARGETPLATFORM
+ARG TARGETARCH
 ARG BUILDPLATFORM
 RUN echo "I am running on $BUILDPLATFORM, building for $TARGETPLATFORM"
 
 WORKDIR /source
 COPY *.csproj .
-RUN case ${TARGETPLATFORM} in \
-         "linux/amd64")  ARCH=x64  ;; \
-         "linux/arm64")  ARCH=arm64  ;; \
-         "linux/arm64/v8")  ARCH=arm64  ;; \
-         "linux/arm/v7") ARCH=arm  ;; \
-    esac \
-    && dotnet restore -r linux-${ARCH}
+RUN dotnet restore -a $TARGETARCH
 
 COPY . .
-RUN  case ${TARGETPLATFORM} in \
-         "linux/amd64")  ARCH=x64  ;; \
-         "linux/arm64")  ARCH=arm64  ;; \
-         "linux/arm64/v8")  ARCH=arm64  ;; \
-         "linux/arm/v7") ARCH=arm  ;; \
-    esac \
-    && dotnet publish -c release -o /app -r linux-${ARCH} --self-contained false --no-restore
+RUN dotnet publish -c release -o /app -a $TARGETARCH --self-contained false --no-restore
 
 # app image
 FROM mcr.microsoft.com/dotnet/runtime:7.0